1. Field of the Invention
The present invention relates to a control apparatus, for an in-vehicle AC generator, that on/off-controls a magnetic-field current in a constant cycle so as to adjust a generation voltage to a predetermined voltage.
2. Description of the Related Art
As a conventional control apparatus of this kind, a control apparatus is known (refer to Japanese Patent Laid-Open No. 1989-218333) in which the operation of a power transistor that controls a magnetic-field current through on/off operation is held by a holding circuit, and the holding state is released by a constant-cycle trigger pulse from a trigger-pulse generator.
In addition, a control apparatus is also known (refer to Japanese Patent Laid-Open No. 1994-113599) in which an adjustment voltage is controlled by an external control signal so that the power-generation amount of an electric generator is variably controlled.
FIG. 7 is a circuit diagram illustrating a control apparatus that has a function, disclosed in Japanese Patent Laid-Open No. 1989-218333, for controlling a magnetic-field current by an inherent-cycle trigger pulse and a function, disclosed in Japanese Patent Laid-Open No. 1994-113599, for variably controlling the power-generation amount of an electric generator by an external control signal; in FIG. 7, reference numeral 1 denotes an AC generator that has an armature coil 101 and a magnetic-field coil 102. Reference numeral 2 denotes a rectifier that has an output terminal 201 and a grounding terminal 202. Additionally, reference numeral 3 denotes a control apparatus (referred to also as a voltage adjuster); voltage-detection voltage-dividing resistors 301, 302, and 328 for detecting the voltage of the output terminal 201 are connected between the output terminal 201 and the grounding terminal 202.
The connection point between the voltage-dividing resistor 301 and the voltage-dividing resistor 302 is connected to the base of a control transistor 304 by the intermediary of a zener diode 303. The output voltage of the AC generator 1 is detected by the voltage-detection voltage-dividing resistors 301 and 302 and the zener diode 303; the control transistor 304 is turned on or off as the zener diode 303 becomes conductive or nonconductive, respectively. The emitter of the control transistor 304 is earthed; the collector of the transistor 304 is connected to a battery 4 by the intermediary of a resistor 306 and a key switch 5 and to the base of a power transistor 305 by the intermediary of a diode 324.
The conductivity of the power transistor 305 is controlled as the control transistor 304 is turned on or off, whereby the magnetic-field current in the magnetic-field coil 102 is controlled; the collector of the power transistor 305 is connected to one terminal of the magnetic-field coil 102 and the emitter thereof is earthed. The collector of the power transistor 305 is connected also to the output terminal 201 by the intermediary of a suppression diode 307; the suppression diode 307 is connected in parallel with the magnetic-field coil 102 so as to absorb an on/off surge produced across the magnetic-field coil 102.
Furthermore, the control apparatus is provided with a transistor 325 whose collector is connected to the collector of the control transistor 304 and whose emitter is earthed and that forms a holding circuit; a voltage-dividing circuit, consisting of a transistor 321 and a resistor 323, which feeds to the base of the transistor 325 a signal for maintaining holding operation of the transistor 325; and a trigger-pulse generator 327 and a transistor 326 that feed to the base of the transistor 325 a signal for releasing the holding operation of the transistor 325.
Meanwhile, from an external control unit 6 that is mounted in a vehicle and receives various kinds of sensor inputs, a signal is inputted to an external-control-signal input terminal C of the control apparatus 3; a transistor 330, which is turned on or off as the foregoing signal exists or not, is connected across the voltage-dividing resistor 328.
Next, the operation of the foregoing circuit will be explained. When, upon the activation of an unillustrated engine, the key switch 5 is closed, a base current is supplied from the battery 4 to the power transistor 305, by way of the key switch 5, the resistor 306, and the diode 324, so that the power transistor 305 is turned on; thus, a magnetic-field current flows in the magnetic-field coil 102, whereby the electric power generator 1 becomes capable of generating electric power.
Next, when the engine is activated, the generator 1 starts generation of electric power, and then the voltage of the output terminal 201 of the rectifier 2 rises. In the case where, at the external-control-signal input terminal C of the control apparatus 3, there exists no signal input from the external control unit 6, whereby the electric potential of the external-control-signal input terminal C is held to be “Hi” (in the case where the transistor 601 is in the nonconductive state), a base current is supplied to the transistor 330 by way of the resistor 329, whereby the resistor 328 is short-circuited as the transistor 330 turns on, and the connection point between the resistor 328 and the resistor 302 is earthed.
In this situation, when the voltage of the output terminal 201 of the rectifier 2 exceeds a predetermined value set with the voltage-detection voltage-dividing resistors 301 and 302 and the zener diode 303, the zener diode 303 turns on, and then the control transistor 304 turns on. Accordingly, the potential of the base of the power transistor 305 becomes the ground potential, whereby the power transistor 305 is turned off; therefore, the magnetic-field current flowing in the magnetic-field coil 102 is reduced, whereby the output voltage of the electric power generator 1 decreases. At this time, because sharing the same base potential with the transistor 305, the transistor 321 is turned off in synchronization with the transistor 305; as a result, due to the voltage produced at the connection point between the resistor 323 and the transistor 321, the transistor 325 is maintained to be conductive.
Next, when the output voltage of the electric power generator 1 decreases to be less than a predetermined value set with the resistors 301 and 302 and the zener diode 302, the zener diode 303 turns off, and then control is performed in such a way as to turn the transistor 305 on. However, as described above, because the transistor 325 is maintained to be conductive, the transistor 321 that operates in the same phase with the transistor 325 is in the nonconductive state; therefore, the power transistor 305 does not immediately turns on.
In order to resolve this condition, a constant-cycle trigger pulse is outputted from the trigger-pulse generator 327, and when the trigger pulse turns the transistor 326 on, the transistor 325 is turned off. That is to say, the trigger pulse finally resolves the condition in which the transistor 325 is maintained to be conductive, whereby the transistor 305 turns on.
In accordance with the foregoing operation, the power transistor 305 of the control apparatus 3 alternately turns on and turns off in a constant cycle, based on the cycle of the trigger pulse generated by the trigger-pulse generator 327, so that the output voltage of the electric power generator 1 is controlled so as to be a first adjustment voltage VHi.
Additionally, in the case where the transistor 601 in the external control unit 6 turns on, whereby the external-control-signal input terminal C of the control apparatus is earthed (connected to the ground with a potential “Lo”)), the transistor 330 is turned off, so that the adjustment voltage is controlled so as to be a value set with the voltage-detection voltage-dividing resistors 301, 302, and 328 and the zener diode 303; therefore, the output voltage of the electric power generator 1 can be controlled with a second adjustment voltage VLo that is lower than the adjustment voltage applied when the electric potential of the external-control-signal input terminal C is “Hi”.
In the conventional control apparatus, for an in-vehicle electric generator, configured as described above, in the case where the signal at the external-control-signal input terminal is fixed to be “Hi” or “Lo” for a long time, the transistor for on/off-controlling the magnetic-field coil can repeat the operation in an inherent constant cycle of the control apparatus so as to perform stable control; however, in the case where, while the signal at the external-control-signal input terminal alternately becomes “Hi” and “Lo”, the control operation is performed, the timing when the trigger-pulse generator generates a trigger pulse so as to turn the power transistor 305 on overlaps, depending on the operation timing, with the timing when the power transistor 305 is turned off by a signal from the external control unit; in this case, there has been a problem that the power transistor cannot be turned on at predetermined timings.
FIGS. 8 and 9 are charts, each representing operation waveforms at various points, for explaining the foregoing problem; FIG. 8 is a chart representing waveforms in the case where the signal at the external-control-signal input terminal is fixed to be “Hi” or “Lo” for a long time; FIG. 9 is a chart representing waveforms in the case where, while the signal at the external-control-signal input terminal alternately becomes “Hi” and “Lo”, the control operation is performed. In the case of FIG. 8, because the signal at the external-control-signal input terminal is fixed to be “Hi” or “Lo” for a long time, the power transistor 305 stably operates in synchronization with a trigger pulse from the trigger-pulse generator 327.
However, in the case of FIG. 9, the signal at the external-control-signal input terminal alternately becomes “Hi” and “Lo”; therefore, in the case where the timing when the external control unit makes the electric potential of the terminal C change to “Lo” so that the adjustment-voltage indication value is reduced to “VLo” and then the power transistor 305 is turned off completely overlaps, as in the portion A, with a trigger pulse from the trigger-pulse generator 327, a case is also caused in which the power transistor 305 cannot turn on at a predetermined timing and operates unstably, whereby the power-generation amount becomes insufficient.